#!/usr/bin/perl -w
use strict;

my $pssum = 0;
open DATA, "/bin/ps -o rss= ax |";
while ( <DATA> ) { $pssum += $_; }
close DATA;

my $memtotal = 0;
my $memfree  = 0;
my $buffers  = 0;
my $cached   = 0;
open DATA, '</proc/meminfo';
while (<DATA>) {
        s/^\s+//;
        my @arr = split(/\s+/);
        if ($arr[0] eq 'MemTotal:')  { $memtotal = $arr[1]; }
        if ($arr[0] eq 'MemFree:')   { $memfree  = $arr[1]; }
        if ($arr[0] eq 'Buffers:')   { $buffers  = $arr[1]; }
        if ($arr[0] eq 'Cached:')    { $cached   = $arr[1]; }
}
close DATA;

my $used = $memtotal - $memfree - $buffers - $cached;
my $diff = $used - $pssum;
print "pssum: $pssum used: $used diff: $diff\n";